A balanced ac bridge has the following constants arm AB, R= 2,000Ω in parallel with C= 0.047μF; arm BC, R=1,000Ω in series with C= 0.47μF; arm BC, R=1000Ω in series with C= 0.47μF; arm CD, unknown ; arm DA, C= 0.5 μF. The frequency of the oscillator is 1,000 Hz. Find the constants of arm CD.